How to implement sending single or group requests?

In Android, libraries for network operations such as Retrofit, Volley, or the standard HttpURLConnection classes are typically used to send single or group requests.

Single request:

• Create a request object with the required URL and parameters.
• Send it asynchronously, and handle the result in a callback.

Group requests:

• Multiple requests can be sent in parallel, using, for example, ExecutorService or library capabilities.
• For sequential sending — launch the next request in the callback of the previous one.
• For parallel processing of results — use CountDownLatch, CompletableFuture, or RxJava.

Example using Retrofit for a single request:

interface ApiService {
    @GET("users/{id}")
    Call<User> getUser(@Path("id") int userId);
}

ApiService api = retrofit.create(ApiService.class);
api.getUser(1).enqueue(new Callback<User>() {
    @Override
    public void onResponse(Call<User> call, Response<User> response) {
        if (response.isSuccessful()) {
            User user = response.body();
            // handle
        }
    }

    @Override
    public void onFailure(Call<User> call, Throwable t) {
        // handle error
    }
});

For group requests, you can launch several such calls in parallel and process the results as they become available.